Conventionally, there has been known a person search system for searching for, on a computer, a desired person in images (moving images) that have been captured or recorded by a monitoring camera or the like by means of an image recognition technique or the like (see, e.g., Patent Documents 1 to 4). Search technology based on the characteristics of the image itself without depending on external information such as tagging is generally called Content-Based Image Retrieval (CBIR), and it also has begun to be used in the search of a person.
Patent Document 1 discloses an image search system and a person search method of cutting out a portion where a person (face) appears from an image, extracting a color histogram or the like as a feature for specifying a person individually, and if the feature is similar to that of a desired person, estimating that the person is the same person as the desired person.
When whether or not the person is the desired person can be determined with a certain degree of accuracy, as in Patent Document 2, by linking images of the same person captured at different times by different cameras, it is possible to track the movement of a person in a much larger area than in the case of one camera, and various applications have been proposed, accordingly. For example, Patent Document 3 discloses an image security system of specifying a movement path of the person by searching captured images, and using the movement path for security management. Also, Patent Document 4 discloses a safety management apparatus for determining whether or not a behavior of a person in a station platform is unusual.    Patent Document 1: Japanese Patent Laid-open Publication No. 2009-027393    Patent Document 2: Japanese Patent No. 4700477    Patent Document 3: Japanese Patent Laid-open Publication No. 2012-068717    Patent Document 4: Japanese Patent Laid-open Publication No. 2010-205191    Patent Document 5: Japanese Patent Laid-open Publication No. 2011-66867    Patent Document 6: Japanese Patent Laid-open Publication No. 2011-210252
As described above, it became possible to understand the behavior of the person by the application of similar image retrieval technique, but the amount of information becomes enormous depending on the number of cameras, images and an accumulation period of features. As in so-called big data, very small part of the information is useful in a monitoring camera system. Sufficient studies have not been conducted on what useful information is extracted based on and how to extract useful information.
Also in an example of detecting a suspicious person by using a security camera, it is difficult to uniquely translate an abstract concept such as “suspicious” by using low-dimensional processing that can be performed by a machine. Even in the case of using a learning machine such as a support vector machine of Patent Document 6 (JP2011-210252A), if re-availability of the learning results cannot be expected, it is not worth an effort to prepare learning data (conditions for detecting a suspicious person).